A man, later known to be Donald Phillipson, goes for an interview in Oxford for the job of headmaster of a school, later known to be the Roger Bacon Comprehensive School in Oxford. At the bus stop a girl gets into conversation with him and later seduces him. She turns out to be a girl from the school, Valerie Taylor, and a year later she goes missing.
Two years after that Inspector Morse picks up the case following a road accident in which Chief Inspector Ainley, who had been investigating the mystery, was killed. A letter arrives apparently from Valerie, but Morse is convinced Valerie must be dead and tries to find out what happened on the day she disappeared. She had gone home from school for lunch that day, and was apparently last seen on her return journey by a lollipop man, carrying a bag and wearing her distinctive school blouse and red socks. Morse suspects she was pregnant and that she had been sent off for an abortion.